The present invention relates to a method for operating a work station of a cheeseproducing textile machine, having the characteristics recited in the preamble to claim 1.
Such cheese-producing textile machines are known, for instance from German Patent Disclosure DE 196 50 932 A1. Such machines, so-called automatic cheese winders, have many work stations embodied as winding stations, which are typically disposed side by side longitudinally of the bobbin winding machine. For control and monitoring purposes, each winding station is assigned a separate work station computer. The individual work station computers are also connected to a central control unit of the bobbin winding machine, via a machine bus.
For supplying and removing tubes and bobbins to and from work stations, such automatic cheese winders typically have a logistics apparatus in the form of a bobbin and tube transport system. In this bobbin and tube transport system, supply bobbins, more commonly known as spinning cops, or empty tubes revolve while standing upright on the mandrels of transport trays.
Such bobbin winding machines also have a service unit in the form of a so-called cheese changer that automatically supplies the work stations. The cheese changer transfers finished fully wound takeup bobbins from the creel of the work station to a transport system of the same length as the machine, which system feeds the cheeses to a transfer station disposed at the end of the machine. The service unit then places a new empty tube in the creel of the applicable work station.
During the rewinding of the yarn from a supply bobbin to a takeup bobbin, it is known to monitor the traveling yarn by means of a tensile yarn force (i.e., yarn tension) sensor and to maintain the tensile yarn force at a predetermined level by means of a yarn tensioner. Thus, by means of the yarn tensioner, a substantially constant tensile yarn force of the running yarn is established, thereby t o assure uniform winding of the yarn on the takeup bobbin.
From German Patent Disclosure DE 41 29 803 A1, it is known to detect the current tensile yarn force of the running yarn using a tensile yarn force sensor. By means of a tensile yarn force measurement, made on the running yarn by this tensile yarn force sensor, a control signal for the yarn tensioner is furnished, and in accordance with the control signal the yarn tensioner exerts a more or less major braking action on the running yarn. To that end, the yarn tensioner has a yarn braking device that can be acted upon by a variable contact pressure. Such a yarn tensioner is known for instance from German Patent Disclosure DE 41 30 301 A1. By the cooperation of the tensile yarn force sensor with the yarn tensioner, it is assured that the yarn is wound onto the takeup bobbin with a defined tensile yarn force.
In the tensile yarn force sensor known from German Patent Disclosure DE 41 29 803 A1, the yarn is guided via a yarn guide element, which is mounted on a head end of a plunger coil disposed in a magnetic field. With this kind of tensile yarn force sensor, a plunger coil current for holding the position of the plunger coil can be taken as a direct variable for the tensile yarn force, since a proportional dependency exists between the tensile yarn force and the plunger coil current. The course of the tensile yarn force can thus be monitored by evaluating the plunger coil current.
In operation of the bobbin winder machine, operating states can occur in which the yarn does not travel in the region of the yarn braking device of the yarn tensioner. For instance, the yarn may travel next to, in front of or behind the yarn braking device. Since this does not directly affect the rewinding process, this incorrect guidance of the yarn is not always directly detectable, but it does have the disadvantageous aspect that the absence of regulation of the tensile yarn force leads to a defective takeup bobbin, which as a rule is wound too softly.
It is therefore an object of the invention to provide a method for operating a work station of a cheese-producing textile machine which overcomes the aforedescribed disadvantages of the prior art and by which high winding quality of the takeup bobbins can be assured.
According to the invention, this object is attained by providing a method for operating a work station of a textile machine for producing cross-wound bobbins utilizing a tensile yarn force sensor connected to a work station computer for monitoring the tensile yarn force of a yarn traveling from a supply bobbin to a takeup bobbin, and a yarn tensioner having a yarn braking device for regulating the tensile yarn force. Briefly summarized, the method basically comprises the operation of the work station computer to execute the steps of predetermining a contact pressure of the yarn braking device of the yarn tensioner acting on the yarn according to the tensile yarn force ascertained by the tensile yarn force sensor, comparing the predetermined contact pressure with a predetermined limit value for the contact pressure, and interrupting the bobbin winding process if the limit value is attained or exceeded for a predetermined time period.
Because the contact pressure of a yarn braking device of the yarn tensioner acting on the yarn is predetermined by the work station computer and is constantly compared with a predetermined contact pressure limit value, it can be ascertained immediately if the instantaneous contact pressure has attained or exceeded the predetermined limit value, and if it has done so for a predetermined time period. In this manner, it is reliably assured that each time the limit value is attained or exceeded over a predetermined time period, the reason for which can for instance be defective yarn guidance, this occurrence is detected immediately, and suitable countermeasures can be initiated. This methodology advantageously prevents a takeup bobbin from being wound too softly and thus defectively as a result of an incorrectly guided yarn. Overall, this method increases the effectiveness of the bobbin winding machine, since early corrective measures can be taken immediately when a problem is detected. The method of the invention also assures that all the takeup bobbins produced will have a substantially constant, high bobbin quality, and in particular will be wound with a constant, defined yarn tension.
In a preferred feature of the invention, it is also provided that the contact pressure of the yarn braking device is monitored during a runup of the bobbin to operating speed after a splicing operation in which the upper and lower yarns have been located and automatically joined. As a result, even immediately after approaching the work station, an incorrect guidance of the yarn, particularly in the region of the yarn tensioner, can be detected. Thus, if the yarn is not guided correctly between the brake disks in the yarn tensioner, this occurrence is detected immediately by the work station computer from the attainment or exceeding of a predetermined contact pressure limit value, and a controlled yarn cut is then performed immediately. Thereafter, a predeterminable length of the yarn is unwound from the takeup bobbin and cut off. Finally, after the lower yarn is rejoined to the upper yarn, the bobbin winding process is continued. As a result of this sequence of steps, a quantity of yarn wound incorrectly onto the takeup bobbin because of incorrect yarn guidance advantageously can be removed from the takeup bobbin immediately. This assures a constant quality of the entire takeup bobbin. It can preferably be provided that after repeated response of the contact pressure monitoring in the runup phase, the work station is shut down and a corresponding malfunction signal is generated.
It is also provided in a preferred feature of the invention that the monitoring of the contact pressure of the yarn braking device is performed during the regular bobbin winding process as well. Thus, if the yarn is travelling at a winding speed of up to 2,000 meters per minute (m/min), proper yarn guidance and thus a defined tensile yarn force can be assured by monitoring the contact pressure of the yarn braking device. Once again, if the contact pressure has attained or exceeded a predetermined limit value for a predetermined time period, a controlled yarn cut is made. A malfunction signal is then generated, which indicates the necessity of checking and/or repair of the applicable work station.
Further preferred features, characteristics and advantages of the present invention will be recognized and understood from the following detailed description of an exemplary embodiment shown in the accompanying drawings.